Two dedicated experiments on internal pair conversion (IPC) of isoscalar M1 transitions were carried out in order to test a 9 MeV/c2 X-boson scenario. In the 7Li(p,e+e-)8Be reaction at 1.1 MeV proton energy to the predominantly T=0 level at 18.15 MeV, a significant deviation from IPC was observed at large pair correlation angles. In the 11B(d,n e+e-)12C reaction at 1.6 MeV, leading to the 12.71 MeV 1+ level with pure T=0 character, an anomaly was observed at 9 MeV/c2. The compatibility of the results with the scenario is discussed.
@article{arxiv.hep-ph/0101298,
title = {Further search for a neutral boson with a mass around 9 MeV/c2},
author = {F. W. N. de Boer and K. Bethge and H. Bokemeyer and R. van Dantzig and J. van Klinken and V. Mironov and K. A. Mueller and K. E. Stiebing},
journal= {arXiv preprint arXiv:hep-ph/0101298},
year = {2009}
}